The present invention relates to an in-line sensing apparatus for sensing interruption of the liquid supply in a line and particularly to a conductivity type in-line liquid sensing apparatus. The prior conductivity type in-line liquid sensing apparatus with which the applicant is familiar utilized a tube of electrically nonconductive material that was connected by electrically conductive end fittings in the liquid supply line to have the liquid flow therethrough with the tube arranged to extend generally horizontally. A low voltage was applied to the end fittings and interruption of liquid supply in the line was sensed by sensing a change in conductivity between the end fittings. However, problems were encountered with occasional bubbles of gas in the liquid which would produce a change in conductivity between the end fittings and cause the sensing apparatus to give a false indication that the liquid supply was interrupted. The addition of an electrically conductive probe that extended from one end fitting into the non-conductive tube and terminated in spaced relation to the other end fitting, did not solve the problem encountered with air bubbles.